The invention relates to an apparatus which is provided in a machine tool for machining gear teeth for the purpose of achieving a tooth flank shape differing from the theoretical shape in the longitudinal direction of the teeth.
An apparatus of this kind for correcting the tooth flanks in their longitudinal direction, for example to a crowned or conical shape, by varying the radial distance of the tool from the workpiece with the aid of a template during the movement of the tool along the tooth has been disclosed in U.S. Pat. No. 3,096,685, in which a template is in contact with a rocker lever which transmits the movement to a threaded spindle and the latter transmits the movement to a wedge slide and to the tool carrier and thus to the tool.
Through the provision of the rocker lever the contours of the template are not reproduced to scale, that is to say in a predetermined ratio, but in a continuously varying ratio, so that for example the desired crowning of the tooth flank cannot be provided on the template simply with an increase of scale (in a fixed ratio) but is determined in a relatively complicated manner in consequence of the changing angular position of the rocking lever in relation to the template at any moment and of the distance between the sensing roller from the centre of rotation of the rocker lever.
An apparatus for producing crowned tooth flanks for bevel gears is also known (DT-PS 855, 495) in which during the longitudinal movement of the tool, wedge-shaped rails are mounted for sliding along a guide surface and the reciprocating movement of the bars for controlling the correction of the tooth flank is derived from a crank drive. Although this arrangement enables the magnitude and position of the crowning to be adjusted, the exact nature of the crowning cannot be adjusted as with a template.
In addition, a gear grinding machine is known (US PS 2, 392, 819) in which for the purpose of producing a deviation from the theoretical longitudinal shape of the tooth, use is made of a template which produces a pivoting motion of a follower fixed to the tool carrier and as in the first-mentioned apparatus has an indirect relationship between the template profile and the tool displacement. In any case, in the grinding of gears much smaller forces occur than, for example, in the planing of gears, this apparatus is suitable only for restricted applications, as in the grinding of gears where there is also only a very slow movement along the template. A rapid but nevertheless accurate cutting sequence with relatively great cutting forces, such as is necessary particularly for gear planing machines, is not possible when this known apparatus is used.